Soft start for five pin switching regulators

• US 4,806,842 A
• Filed: 05/09/1988
• Issued: 02/21/1989
• Est. Priority Date: 05/09/1988
• Status: Expired due to Term

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Bittner, Harry J.
• Primary Examiner(s): Beha, Jr., William H.
• Application Number:
  US07/191,463
• Time in Patent Office: 288 Days
• Field of Search: 363/49, 323/222, 323/284, 323/288, 323/901, 307/265
• US Class Current: 323/222
• CPC Class Codes: H02M 1/36 Means for starting or stopping converters
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators
• CPC Class Codes: Y10S 323/901 Starting circuits

Abstract

A soft start circuit for a switching regulator is disclosed. The circuit does not require any off-chip parts and, therefore, a five-pin package can be employed. The operation of a soft start circuit in conjunction with a switching regulator operating in the voltage boost mode is set forth in detail.

Claims

1. A switching regulator including a switch, means for driving said switch in a controlled duty cycle fashion in response to the output of a duty cycle comparator, an error amplifier driving said duty cycle comparator, a compensation capacitor and means for developing a reference potential against which said error amplifier operates, a soft start circuit comprising:

R-S flip flop means having set, reset and output terminals;

means for resetting said R-S flip flop when said compensation capacitor is discharged;

a soft start comparator having an output coupled to said set terminal of said flip flop, an inverting input coupled to said reference potential, a noninverting input coupled to said error amplifier input whereby said R-S flip flop is set when said error amplifier input exceeds said reference potential;

switch means coupled in series with the output of said error amplifier and responsive to said output to said R-S flip flop for disconnecting said error amplifier when said R-S flip flop is reset; and

a current source coupled to charge said compensation capacitor at a controlled rate controlled by said output of said R-S flip flop to be one when said R-S flip flop is reset.

2. The switching regulator soft start circuit of claim 1 further including a shutdown circuit responsive to either excessive integrated circuit chip temperature or low power supply output voltage to reset said R-S flip flop, said shutdown circuit operating to close a switch connected across said compensation capacitor.

3. The switching regulator soft start circuit of claim 2 further including a power up comparator responsive to the charge on said compensation capacitor and operatively coupled to reset said R-S flip flop when said charge falls below a predetermined fraction of said reference voltage.

4. The switching regulator soft start circuit of claim 3 wherein said power up comparator output and said shutdown circuit are coupled to said reset terminal of said R-S flip flop by means of an OR gate.

5. The switching regulator soft start circuit of claim 1 wherein said switching regulator is in the form of an integrated circuit having a power input pad, a ground pad, a compensation capacitor pad, a switch terminal pad, and a feedback pad mounted in a five pin power package.